Documentation: Add basic flashing tutorial for Lenovo

* Add basic flashing tutorial
** Describe internal and external flashing
** Describe flash supply diode protection
** Gives general advices on flashing
** Describe how to use flashrom --ifd
*  Describe basic flashing on Lenovo T4xx devices
** Describe how to disassemble and access the flash IC on T4xx
** Describe flash layout on Sandy Bridge and Ivy Bridge series.

Change-Id: Ia833e27f4e7d89ee32be9bed21a0c021839facec
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/27852
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

Documentation/flash_tutorial/int_flashrom.md

@@ -0,0 +1,19 @@
+# Flashing firmware internally
+
+**WARNING:** If you flash a broken firmware and have no recovery mechanism, you
+             must use the **external method** to flash a working firmware again.
+
+## Using flashrom
+This method does only work on Linux, if it isn't locked down.
+You may also need to boot with 'iomem=relaxed' in the kernel command
+line if CONFIG_IO_STRICT_DEVMEM is set.
+
+
+For more details please also check [flashrom's wiki].
+Use the programmer *internal* to flash *coreboot.rom* internally:
+
+```bash
+flashrom -p internal -w coreboot.rom
+```
+
+[flashrom's wiki]: https://www.flashrom.org/Flashrom